1. Field of the Invention
The present invention generally relates to semiconductor devices, and more particularly to a ball grid array (BGA) semiconductor device having improved electromagnetic interference (EMI) characteristics.
2. Discussion of the Related Art
A variety of packaging styles are known for semiconductor devices. Dual in-line packages (DIPs), pin grid arrays (PGAs), and surface mount packages are examples of several semiconductor package styles. These package styles, however, become problematic at higher operating frequencies.
More specifically, at high frequencies even the relatively short leads of standard surface mount, or through hole mount, integrated circuit (IC) packages tend to act like antennas, radiating electromagnetic fields outwardly therefrom. Even home computers today operate at clock speeds of 300 Mhz or higher. Other, specialized computing devices operate at even higher speeds. The high frequency signals input to and output from an IC pass across the chip leads. Longer package leads results in a more severe "antenna " effect and thus more intense EMI.
As is known, EMI is disruptive to the proper operation of other circuit components proximately located to the source of the EMI. Accordingly, there is an identifiable need to reduce the levels of EMI generated. As is further known, this may be achieved by reducing the lead length of integrated circuit components. Ball grid array (BGA) packages are a known package style that have a lessened radiation of EMl because of much shorter lead length.
BGA packages connect to a PC Board through an array of solder balls beneath the packages. The area array reduces package size and increases lead pitch, leading to higher assembly yields. More particularly, a BGA is a type of packaged integrated circuit in which one or more integrated circuit chips are mounted on a surface of a substrate, and electrical connection to electrically conductive material not part of the packaged integrated circuit, such as a printed circuit board, is made by an array of solder balls located on a surface of the substrate opposite the surface to which the integrated circuit chip or chips are attached. The integrated circuit chip or chips and the passive components are typically encapsulated by, for instance, plastic to protect the integrated circuit chip or chips and the passive components from the external environment. The integrated circuit chip is electrically connected to the substrate by wirebonding, tape-automated bonding, or flip-chip interconnection. BGAs allow a high density of external chip connections to be made as compared to other packaged integrated circuits having leads extending from the package.
Flip chip interconnect technology supports "area array interconnect," in which the die is mechanically and electrically connected through an array of solder bumps on the active face of the circuit. This technique increases the number of connections that can be made for a given die size and can also improve electrical performance. The die is attached to the substrate face down and is typically reinforced with an epoxy underfill.
From a manufacturing point of view, BGA packages have many virtues. A BGA package can pack the same processing power as a QFP package into 40 percent less volume, making BGA chips thinner and lighter. BGA also offer designers flexibility, allowing them to maximize the density of connections per chip to improve high-frequency operation.
Even with the shorter lead length of BGA packages, however, the high frequency operation of many modern electronic devices may still generate unacceptable levels of EMI. Accordingly, it is desired to provide an improved semiconductor package that results in lower levels of EMI.